Jude Law and Damon Albarn have joined hundreds demonstrating in London over piracy charges brought by Russia against 30 Greenpeace activists.
Six British activists were among those arrested last month as they protested against oil drilling in the Arctic at a rig owned by Russian firm, Gazprom.
Relatives of the activists protested outside Russia’s London embassy.
It was one of a number of events being held in more than 40 countries.
The entire crew of the ship, Arctic Sunrise, was arrested on September 18 after two activists tried to board the Russian state-controlled oil platform in the Pechora Sea.
They have all been charged and are being held in the port of Murmansk, in northwest Russia, facing prison terms of up to 15 years.
The Britons who have been charged include freelance video producer, Kieron Bryan, and logistics co-ordinator, Frank Hewetson – both from London.
UK activists Anthony Perrett from Newport in Wales; Alexandra Harris, originally from Devon; Philip Ball from Chipping Norton; and Iain Rogers, from Exeter, have also been charged.
In London, Saturday’s protesters stood behind banners declaring, “Free the Climate Defenders”, “Journalist and Not Pirate”, and “Free The Arctic 30”.
Jude Law, who knows Frank Hewetson, said he was “exercising my right to peacefully protest”.
He added: “I am just adding my face and body to the mass of support. What is ludicrous is that they have been charged with piracy.”
Actors Imelda Staunton and Jim Carter also turned up in front of the embassy in west London to show their support for the activists.
Jim Carter described the arrests as “a ludicrous situation” and urged PM David Cameron – along with the leaders of the other 18 countries which made up the nationalities of the 30 activists – to apply pressure on Russia.
Foreign Secretary William Hague has raised the case with his Russian counterpart and said British officials would continue to raise specific concerns Greenpeace had about the legal process with Moscow.
The Netherlands has also launched legal action to free the activists. Two of its citizens are among those charged, along with people from countries including Argentina, Australia, Canada, France, New Zealand, Russia, and the US.
Other Greenpeace protests took place in cities including Madrid, Moscow, Mexico City, Sao Paulo and Istanbul.